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Current-vollaqe characteristic cunro o! the new diodę.

”Tunnel Diodes”

EXPERIMENTAL SEMICONDUCTORS

lnsensiłive to temperaturę changes and 100 times faster than today's transistors, these devices bear watching.

THE ncwest "baby" in the fast-growing family of semi-conductor dcviccs—the "tunnel diodę"—is coming of age. The new device, first reported in 1958 by Japanese scien-tist Leo Esaki, is closer to commercial application as a result of intensive research programs at G-E and other com-panies. The special diodę is a heavily doped junction semi-conductor that has a negative-resistance characteristic over part of its operating rangę (see the graph above>.

The tunnel diodę takes its name from the physical phenomenon that makes it possible: "quantum-mechanical tunneling.” The term is used to describe the manner in which the electrical charges move through the device. Such motion takes place with the speed of light, in contrast to the relatively slow motion of electrical charge carriers in transistors. These high speeds make it possible for the device to operate at extremely high frequencies. Oscillation higher than 2000 mc. has already been obtained and fre-quencies of morę than 10.000 mc. are expected in the near futurę.

This high-speed response also suggests applications in computers. When used as switches, tunnel diodes have functioned in a fraction of a millimicrosecond—from 10 to 100 times faster than the fastest transistor now available.

The device also resists the damaging efTects of nuclear radiation. Because it is less dependent on the structural perfection of its crystal than is the transistor, it is much less affected by the damage that radiation can do to such crystal structures. In this respect it outranks transistors by morę than 1000 to 1. Materials used for tunnel diodes include Silicon, germanium, gallium arsenide, gallium anti-monide, and indium antimonide. Silicon tunnel diodes work at temperatures 250°F higher than temperatures at which conventional Silicon diodes and transistors operate.

The negative-resistance characteristic allows the unit to be used as an amplifier, a generator of r.f. power, and a switching device. Its simplicity makes possible the devel-opment of integrated circuits. It is superior to vacuum tubes and transistors for applications in low-noise amplifiers and mixers for high frequencies. Many parametric amplifier jobs. for example, could be performed morę easily with tunnel diodes.

G-E now has plans to offer limited quantities of experi-mental samples in the next few months.

ANestled inside a paper dip. a tunnel diodę U ihown in close-up riew. Connecting wire leads to alloy soldered to germanium crystal which is soldered to metal piąte.

Vest-pocket transmitter. malcing use of a tunnel diodę, and with a rangę ot about onehalf mile. is demonstrated by G E scientists. At left. Dr. Guy Suits. G-E rice-president and director of research. speaks into microphone. while Dr. lerorae Tiemann holds the transmitter. In foreground. ordinary FM receirer picks up slgnal.

A complete tunnel diodę transmitter is compared in sise with a ► 50-cent piece. The transmitter consists of one rariable and two fixed ceramic capacilors. a coil that tunes to the operating frequency —which may be higher then 2000 mc.—and the diodę itseli. located inside the “can“ In the center of the derice. Battery is not shown.

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October. 1959